Numerous types of safety valves and kelly valves have been devised over past decades. These valves are commonly used in oilfield operations to control the internal pressure in tubing. A safety valve is commonly located adjacent the rig floor, and a kelly valve conventionally receives a kelly and is located above the rig floor. While a blow-out preventer provides safety from well pressure in the annulus about the tubing string, the safety valve provides safety from internal tubing string pressure. Some safety valves are hydraulically or pneumatically operated, although mechanically operated safety valves are highly preferable for many applications due to their simplicity and high reliability. Mechanically operated safety valves may be controlled by surface operations, and the valves may be used on the surface or downhole below the rig floor to control tubing string flow.
A significant problem with mechanically operated safety valves is that the high internal fluid pressure within the tubing string and therefore within the valve acts upon the trunnions which form the rotatable axis or stem of the ball. These high forces cause significant frictional engagement between the rotating ball and the body of the valve, thereby detracting from the reliability of the valve, particularly under high pressure applications. High pressure forces on the valve may thus stop the valve from opening.
Various types of safety valves include an actuator, as disclosed in U.S. Pat. No. 4,270,849. U.S. Pat. No. 4,340,008 discloses a pressure balanced safety valve, and U.S. Pat. No. 4,550,980 discloses a safety valve with a lock mechanism. A safety valve for coiled tubing is the subject of U.S. Pat. No. 6,742,597. A safety valve which uses a flapper is disclosed in Publication 2005/0039922. Safety valves with ball valves are highly preferred over safety valves with other types of valve closure members.
Various other patents disclose improvements to valves, and in particular to safety or kelly valves. These patents include U.S. Pat. Nos. 4,310,051, 4,340,080, 4,303,100, 4,462,693, 4,476,935, 4,625,755, and 4,969,515. More recent patents of interest include U.S. Pat. Nos. 6,289,911 and 6,640,824. Additional publications include 2002/0066486, 2001/0037900, 2003/0056829, 2004/0045722, 2006/0184139 and 2002/0066486.
The disadvantages of the prior are overcome by the present invention, and an improved safety valve and method of actuating a safety valve are hereinafter disclosed.